EP0259168B1

EP0259168B1 - New water-soluble salts of thionapthene-2-carboxylic acid

Info

Publication number: EP0259168B1
Application number: EP87307807A
Authority: EP
Inventors: Carlos M. Samour; Stefanos Daskalakis; James R. Marshall
Original assignee: Macrochem Corp
Current assignee: Macrochem Corp
Priority date: 1986-09-03
Filing date: 1987-09-03
Publication date: 1991-12-11
Anticipated expiration: 2007-09-03
Also published as: FR2603281A1; IT1218161B; DE3775147D1; IT8748347A0; CA1327807C; EP0259168A1; ES2037722T3; FR2603281B1

Description

This invention relates to thionapthene-2-carboxylic acid (TNCA) water-soluble salts (TNSA) (Also called Benzo(b)thiophene-2-carboxylic acid salts), and processes of making and using these compounds.

BACKGROUND OF THE INVENTION

Osteoporosis is a common and progressive condition occurring in adults which results in a decrease in bone throughout the body. This loss includes the mineral portion of the bone, which is a calcium phosphate material called "hydroxyapatite", as well as the matrix, which is a protein called "collagen". Osteoporosis may begin in early adulthood and progress, inexorably, to middle age and old age with manifestations running the gamut of moderate to severe pain along with X-ray evidence of bone loss and/or deformation to eventual brittleness which we see evidenced, for example, in older people who so easily break a hip bone from a simple, and seemingly not dangerous, fall. It has been stated that osteoporosis is the most common cause of fractures in people over the age of 65.
While the causes of osteoporosis are not well understood and, in many cases quite obscure, it is believed that there is an imbalance between bone production and bone resorption (i.e., bone breakdown).
During the life of an animal, new bone is continuously being formed and old bone resorbed. In osteoporosis, resorption exceeds bone formation.
Present methods for treating osteoporosis are far from satisfactory. Such treatments include the administration of calcium salts, fluorides, calcitonin, estrogens, Vitamin D, and anabolic agents, among others. Anabolic agents and estrogen therapy have been the therapy of choice for osteoporosis in post-menopausal women. Such treatments appear to entail an increased risk of uterine and breast cancer. Other treatments still remain to be proven including the Physical Therapy approach.
Among the newer approaches to the treatment of osteoporosis has been the use of materials with hypocalcemic activity, i.e., lowering of the serum calcium, which is believed to be related to and indicative of a decrease in the rate of bone resorption. Calcitonin, mithramycin (an antibiotic) and certain phosphonates are representative hypocalcemic agents, but adverse effects and lack of effectiveness in bone-loss prevention associated with the use of such agents, make continued research necessary.
In recent U.S. Patents 4,101,668 (issued July 18, 1978), 4,125,621 (issued November 14, 1978) and 4,185,108 (issued January 22, 1980), all three having as inventors C. M. Samour and J. A. Vida, there are disclosed a wide variety of benzo-heterocyclic compounds for use as antiosteoporotic agents. Among the specific compounds described are thionaphthene-2-carboxylic acid, thionaphthene-3-carboxylic acid, thionaphthene-4-carboxylic acid, dibenzothiophene-4-carboxylic acid, thioxanthene-9-one-4-carboxylic acid and indole-2-carboxylic acid.
The compounds are compared to thyrocalcitonin (TCT), the latter, a bond-remodeling hormone which is capable of reducing bone resorption rates. In the patented disclosures, the effectiveness of any bone resorption modifying agent is determined by measuring the effect on the production of cyclic adenosine-3ʹ5ʹ-monophosphate (c-AMP) using the methods of Rodan et al, J.B.C. Vol 429, page 306, 1974; Rodan et al, Science, Vol. 189, page 467, 1975. In the comparison, the activity shown by the free acid compounds covered by the disclosure of the aforementioned patents ranges from slightly more than half as effective to twice as effective as TCT in stimulating the production of c-AMP.

Prior Art

The U.S. Patents (to Samour et al) 4,101,668, 4,125,621 and 4,185,108 mentioned in the "Background" to the present invention constitute the only significant Prior Art to which we are aware.
In the patents, mention is made that the "pharmaceutically acceptable salts include the non-toxic metallic salts such as sodium, potassium, calcium and aluminum, the ammonium salt and substitued ammonium salts, e.g., salts of such nontoxic amines as trialkylamines including thiethylamine "--(presumably triethylamine is intended)--" L-lysine, procaine, dibenzylamine, N-benzyl-beta phenylethylamine, L-ephenamine-N,Nʹ dibenzylethylenediamine, N-(lower) alklypiperidine, e.g., N-ethylpiperidine", but no specific salt is given. The studies shown in the patent were done in vitro and in vivo but the latter were conducted by injecting the drug. In Example 5 of each patent, benzo(b)thiophene-2-carboxylic acid was used for 3 days (1 mg/day by subcutaneous (S.C.) injection. In Example 6 the dose was reduced to 200 ug/day and in Example 7, the drug was injected for 10 days (S.C. 1 mg/day).
In other studies it has been found that in acute toxicities in rats and monkeys, using TNCA in gum tragacanth, the oral LD₅₀ in mice is 3.6 g/kg whereas when injected subcutaneously, the LD₅₀ in mice is 1.45 g/Kg, indicating a low response level to the orally ingested drug.

Description of the Present Invention

The present invention provides new salts of benzo(b)thiophene-2-carboxylic which are readily prepared in high yields, which are particularly free of irritating side effects in the stomach as well as other untoward effects when taken orally, and which give rise to rapid and clinically-response-effective blood levels via the oral route. The LD₅₀ of the water-soluble salts of this invention and particularly the L-lysine salt when given orally is almost equivalent to that obtained when administered intraperitoneally.
The specific salts with which this invention is concerned are the L-lysine salt and the L-arginine salt.
Surprisingly, these salts are easily prepared, readily isolated, obtainable in good yields, and water-soluble. This is to be contrasted with other salts which would suggest themselves, namely, the sodium salt, potassium salt, glycine salt, L-alanine salt, L-proline salt and even the triethylamine salt. As a matter of fact so suggestive a salt as the potassium and sodium salts have proven difficult to prepare and when made are mainly insoluble in water. In this regard, it is to be noted that while the ammonium salt (not of the present invention) is simply and conveniently made by merely mixing even dilute ammonium hydroxide solutions with the solid free acid (benzo(b)thiophene-2-carboxylic acid) and evaporating the water to isolate the ammonium salt, solid TNCA when mixed into aqueous caustic soda solutions is totally unaffected and unreactive to form the sodium salt; this is true with 8% (2N) and with 20%, 40%, and 60% aqueous solutions. This is also the case when one uses aqueous sodium carbonate. Considering that the pK of the TNCA is 3.4, this action is quite strange. The L-lysine salt is also made in the same simple and efficacious manner as the ammonium salt, again by the incremental addition of the TNCA to an aqueous solution of L-lysine. The use of solutions of both reactants in a suitable solvent such as methanol may be used with facility since the TNCA compound is soluble in methanol. In contrast, the sodium salt is produced only when one utilizes sodium ethoxide in methanol or sodium hydroxide in a mixture of alcohol and water. The formation of the sodium salt was demonstrated by means of infra-red spectroscopy and also the fact that it does not melt. Similarly, the potassium salt could not be formed by treatment with aqueous potassium hydroxide. However, the potassium salt of TNCA is formed when excess potassium hydroxide and TNCA are added to a warm solution of methanol containing a small amount of water.
The utility of the salts, in a clinical treating sense, is equivalent to TNCA itself but they are far more useful, practically, for the reasons of amelioration of side effects and the high blood levels available via the oral route.
As examples, TNCA, as an acid in high concentrations, causes gastric irritation, resulting in vomiting and bleeding. On the other hand, TNCA lysine salt acts as an effective buffer, hence prevents the adverse effects associated with gastric irritation.
More importantly, TNCA is poorly absorbed from the gastrointestinal tracts; as mentioned earlier, the oral LD₅₀ is 3.6 gm/Kg., whereas by injection, this value is only 1.45 g/Kg. In marked contrast, the oral dose of the TNCA lysine salt is roughly 1.5 g/Kg and, by injection, is not significantly different (approximately 1.3 g/Kg). This finding that TNCA lysine salt is equally effective when given orally or by injection, indicates that the lysine salt, in contrast to TNCA, is readily absorbed following oral administration.
The following examples will serve to illustrate the present invention without being deemed limitative thereof. Parts, when used, are by weight, unless otherwise indicated.

Example 1

Preparation of Benzo(b)thiophene-2-carboxylic acid L-Lysine salt:

95.02 g (0.65 mole) of L-lysine is dissolved in 637 ml. of water. To this solution is added, in small portions, 115.83 g (0.65 mole) of TNCA (m.p. 237-238°C) and the reaction mixture is stirred at 50°C for one hour. The mixture is then filtered and the water is removed from the filtrate to give a pinkish white solid of the above formula and with a melting point of 240-242°C. The salt is highly (70%) water-soluble. A 5% aqueous solution of the salt has a pH of 5.75. It is insoluble in methyl alcohol, ethyl alcohol and toluene.
A solution is prepared by mixing a solution of 447 mg of triethanolamine (0.003 mole) in 15 ml of methanol with another solution of 537 mg (0.003 mole) benzo(b)-thiophene-2-carboxylic acid (TNCA) in 5 ml of methanol. The solution is filtered and the solvent is removed from the filtrate to give 850 mg of a white water-soluble solid, m.p. = 144-148°C. A 5% aqueous solution of the salt has a pH of 6.77.

Example 2

Preparation of the Arginine salt of TNCA:

To a solution of 2.97 g (0.016 mole) of L-arginine in 18 ml of water is added, while being stirred, 3 g (0.016 mole) solid TNCA. The mixture is stirred at 40°C until all TNCA dissolves. The water was removed in vacuum. 5.6 g of a white, water-soluble solid, m.p. = 55°-60°C., is obtained. A 5% aqueous solution of the salt has a pH of 5.8. The salt is also soluble in methanol and ethanol.

Example 3 (Comparative)

Preparation of the Sodium salt of TNCA:

108 mg (0.002 mole) of sodium ethoxide in 6 ml methanol is mixed with 358 mg (0.002 mole) of TNCA in 10 ml of methanol. 321 mg of a white water-insoluble salt is obtained on removal of the methanol from the almost clear solution. The solid does not melt below 300°C and the IR spectrum clearly indicates the presence of a salt.

Example 4 (Comparative)

Following the procedure of Example 6, 203 mg (0.002 mole) of triethylamine is dissolved in 4 ml of methanol and mixed with 358 mg (0.002 mole) of TNCA in 10 ml. of methanol. A water-insoluble liquid results.

Example 5 (Comparative)

Following the procedure of Example 1, L-alanine, L-glycine, and L-proline are used, in equivalent amounts in place of L-lysine. No water-soluble reaction product is formed.
The following tables (Experiments I and II) illustrate the effectiveness of the present invention in reducing the blood calcium levels of rats made hypercalcemic by the injection of Leydig-cell carcinoma-tumor material. For details of the methodology employed in these studies, see: Johannesson et al., Endocrinology 117/4: 1508-1511 (1985). Normal calcium blood levels are in the range of 9-10 mg/dL.

Calcium Serum Concentrations

Table I

(Experiment 1)
Measure	Group	N	Mean	S.D.
Initial	Control	5	11.22	1.68
Calcium	195 mg/kg	8	12.28	1.71
Levels	292 mg/kg	9	13.31	3.32
Final	Control	5	17.38	3.71
Calcium	195 mg/kg	8	14.85	3.56
Levels	292 mg/kg	9	11.54	2.54

Table II

(Experiment 2)
Measure	Group	N	Mean	S.D.
Initial	Control	6	15.17	2.26
Calcium	195 mg/kg	6	14.07	2.33
	292 mg/kg	6	14.68	2.56
	389 mg/kg	10	13.80	2.70
Final	Control	6	18.03	2.14
Calcium	195 mg/kg	6	13.27	2.07
Levels	292 mg/kg	6	11.00	1.30
	389 mg/kg	8	10.16	0.49

The data in Tables I & II show that the initial serum concentrations of calcium are considerably higher than normal for the rat, ranging from 11.22 to 13.31 mg/dL (mg per deciliter) in Experiment 1 and from 13.80 to 15.17 mg/dL in Experiment 2. In the table, n = number of rats evaluated at each dosage and in controls while S.D. = standard deviation. These higher initial values reflect Leydig cell-induced hypercalcemia. Data for final calcium levels show the decreases in calcium levels produced following administration of the lysine salt of TNCA. Such decreases are clearly dose-related in both experiments, dropping from control values of 17.38 to 11.54 in Experiment 1, and from 18.03 to 10.16 in Experiment 2, corresponding to doses of 292 mg/Kg and 389 mg/Kg, respectively. It is noteworthy that the serum calcium levels following treatment with the lysine salt of TNCA returned to pretreatment levels, but not to below normal values, i.e., not below calcium concentrations present before the development of Leydig cell tumors. This indicates that the lysine salt of TNCA is anti-hypercalcemic, rather than hypocalcemic. The distinction is important since the objective of therapy with this drug is to lower calcium significantly, but not to levels that would cause the adverse effects of hypocalcemia.
Particularly useful for patient use are pharmaceutically acceptable liquid dosage forms incorporating TNCA and they may be prepared by utilizing the teachings exemplified above regarding the formation of salts of TNCA with TNCA as the acid. The base is chosen from the class of lysine and arginine.
Liquid dosage forms may be prepared either by the dissolution of the isolated salt into water, by the dissolution of TNCA into an aqueous solution containing lysine or arginine salts, or by the simultaneous dissolution of TNCA and the free base into an aqueous medium.
The following are suggested dosage formulations:
In the liquid oral dosage form, one ml of the solution may contain 15-1000 mg of TNCA, as the salt of lysine and/or arginine. Also contained in the solution may be sodium chloride for the purpose of achieving isotonicity, sodium hydroxide for pH adjustment (preferably 6 to 8), and phosphate buffer to maintain pH. Also included may be a preservative, a humectant, a flavor, and a color.
A pharmaceutically acceptable liquid oral dosage form containing salts of TNCA may also be prepared as a combination solution/suspension, in which a portion of the TNCA salt is dissolved and the remainder is suspended. The preparation may contain 15-1000 mg of TNCA per ml as the salts of lysine or arginine. The body of the preparation may consist of distilled deionized water into which a portion of the salt is dissolved, and a water-miscible vehicle which is used as the supporting medium for the suspended TNCA salt. This formulation would also contain sodium chloride, sodium hydroxide, and a phosphate buffer as well as a suspending agent, a flavor, and a color.
Another pharmaceutically acceptable liquid oral dosage form containing TNCA may also be prepared as an emulsion. The preparation may contain 15-1000 mg of TNCA per ml as the salts of lysine or arginine. The body of the preparation may consist of distilled deionized water and a vegetable oil properly emulsified with an emulsifying agent such as lecithin, pluronics, tweens, brijs, or arlacels, etc., as needed to produce a stable W/O emulsion of the water solution of the TNCA salt in the external oil phase. Also included may be sodium chloride, sodium hydroxide, phosphate buffer, preservative, humectant, flavor and color.
Liquid oral dosage forms may offer advantages in certain patients and in certain applications. Patients unable to swallow large solid dosage forms would be particularly good candidates for a liquid dosage form. Liquid dosage forms may also allow larger amounts of drug to be administered in a manner that promotes patient compliance.
It is also contemplated that a liquid dosage form may be used parenterally (by injection) either by I.V., S.C. or I.M. In the case of an injectable or parenteral liquid dosage form, one ml of solution may contain, in part, 15-1000 mg of TNCA as the salt of lysine or arginine. Also contained in the solution would be a salt such as sodium chloride for the purpose of achieving isotonicity; sodium hydroxide for adjustment of pH as needed (preferably to within the range 6 - 8); phosphate buffer; a preservative if needed; and U.S.P. Water For Injection.
The following are specific exemplifications within the formulations of Examples 9 to 12.

Example 11

Injectable (I.V., I.M., S.C.) - Single Dose
TNCA	400 mg
l-lysine	328 mg
sodium chloride, U.S.P.	5 mg
sodium hydroxide, U.S.P.	0.1 mg
phosphate buffer (pH 7.0)	0.5 ml
water for injection, U.S.P. q.s.a.d.	5.0 ml

Example 12

Injectable - Multiple Dose
TNCA	400 mg
l-lysine	328 mg
sodium chloride, U.S.P.	5 mg
sodium hydroxide, U.S.P.	0.1 mg
phosphate buffer (pH 7.0)	0.5 ml
Thimerosol	0.05 mg
water for injection, U.S.P. q.s.a.d.	5.0 ml

Example 13

Oral Solution
TNCA	600 mg
l-arginine	586.5 mg
sodium chloride, U.S.P.	2.0 mg
sodium hydroxide, U.S.P.	0.2 mg
potassium sorbate, U.S.P.	0.05 mg
phosphate buffer (pH 7.0)	3.0 ml
glycerine, U.S.P.	100 mg
saccharin sodium, U.S.P.	0.5 mg
natural strawberry flavor	0.05 ml
FD&C Red #40	0.0001mg
distilled deionized water q.s.a.d.	10.0 ml

Claims

A water-soluble compound selected from the lysine and arginine salts of thionapthene-2-carboxylic acid (TNCA).
A method for making a compound as claimed in claim 1 which comprises mixing thionapthene-2-carboxylic acid with a solution of the salt-forming base.
A method as claimed in claim 2 wherein the base is lysine and it is dissolved in a suitable solvent.
A method as claimed in claim 3 wherein the solvent is an alcohol.
A method as claimed in claim 4 wherein the TNCA is in solution in an alcohol prior to mixing with the salt-forming base.
A method for preparing an aqueous solution of the lysine or arginine salt of thionapthene-2-carboxylic acid which comprises mixing the solid acid in an aqueous medium with lysine or arginine whereby an aqueous solution of the lysine or arginine salt is formed in situ.
A pharmaceutical composition comprising a compound as claimed in claim 1.
A pharmaceutical composition suitable for oral administration comprising an aqueous solution of a compound as claimed in claim 1.